Estudo Geralhttps://estudogeral.sib.uc.ptThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 07 Jun 2020 09:56:32 GMT2020-06-07T09:56:32Z50201Transient behaviour and rate effects in resistive detectorshttp://hdl.handle.net/10316/4561Title: Transient behaviour and rate effects in resistive detectors
Authors: Fraga, M. M.; Marques, R. Ferreira; Ivaniouchenkov, Y.; Lima, E. P. de; Neves, F.; Policarpo, A. J. P. L.; C. Bueno, Carmen; Gonçalves, Josemary A. C.; Santos, M. Damy de S.; Costa, L.; Mendiratta, S.; Monteiro, J. H.
Abstract: The dependence of the detection efficiency (or charge gain) of a resistive detector on the counting rate has been considered by several authors. The influence of the resistivity of the electrodes, the counter geometry and the gas mixture composition have also been studied. Most of those measurements assume a stationary regime. In the present work we report on studies of the transient behaviour of detectors with a resistive cathode for various counting rates, charge gains and detector geometries. We show that in some cases the time-decay curves can be fitted by a single exponential plus a constant term, while in others (higher charge gains or higher counting rates) a sum of two or even three exponentials plus the constant term is needed to fit the experimental data. A study of the electric properties of the dielectrics used is also presented and a comparison is made between these results and the data obtained under irradiation conditions.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10316/45611998-01-01T00:00:00ZRate effects in a proportional counter with resistive cathodehttp://hdl.handle.net/10316/4568Title: Rate effects in a proportional counter with resistive cathode
Authors: Bueno, Carmen C.; Fraga, M. M.; Gonçalves, Josemary A. C.; Marques, R. Ferreira; Policarpo, A. J. P. L.; Santos, M. Damy de S.
Abstract: In this work, the rate effects associated with the gain of detectors with resistive electrodes are considered. To study these effects it was decided to use the classical proportional counter geometry, with a cylindrical glass tube as the cathode, rather than parallel plate devices. Indeed, the generality of the information obtained is not affected and the cylindrical proportional counter geometry has several advantages to gather detailed experimental data and to compare it with simple electric field calculations. A self-consistent set of data is presented for the effects of counting rate from a few tens of Hz up to several hundreds of Hz, using several gas mixtures, different anode wires, cathode radii and thickness of the resistive electrodes. Although a few sources of systematic errors can be identified, all the observed experimental data can be quantitatively explained. Indeed, the measured gas amplification, from a few tens up to ~5×104 and for the range of counting rates quoted above, depends only on the local electric field as it should be expected. These results are directly relevant to approach the problem of counting efficiency in resistive plate chambers.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10316/45681998-01-01T00:00:00ZEffect of the drift field on avalanche gain and charge collection in microgap detectors at high pressurehttp://hdl.handle.net/10316/4560Title: Effect of the drift field on avalanche gain and charge collection in microgap detectors at high pressure
Authors: Fraga, F. A. F.; Marques, R. Ferreira; Gonçalves, J. A. C.; Gonçalo, J. R.; Policarpo, A. J. P. L; Eijk, C. W. E. van; Hollander, R. W.; Berg, F. van den
Abstract: One of the main drawbacks of the use of microgap structures when used at high pressure (6 bar) at high count rates (~106 s-1 mm-2) is the limited maximum safe gain at which they can be operated. The use of a preamplification device such as the GEM (gas electron multiplier) can overcome this limitation; however, secondary space charge effects due to charge accumulation at the non-metallic surfaces cannot be neglected and should be minimised. These positive charges are due to the intrinsic multiplication of the GEM device and also to the drift of ions from the anode of the main detector. In this study we present data on the variation of the positive ion collection by the drift electrode versus drift field at several pressures up to 6 bar using a Kr-CO2 mixture. Data were collected with microgaps having several anode and insulator widths. The influence of the drift field in the pulse rise time is also considered.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10316/45601998-01-01T00:00:00ZDead Region Time Evolution and Afterpulses Development in SQShttp://hdl.handle.net/10316/12905Title: Dead Region Time Evolution and Afterpulses Development in SQS
Authors: Lima, E. P. de; Salete, M.; Leite, S. C. P.; Policarpo, A. J. P. L.; Alves, M. A. F.
Abstract: The dead length, 6, for t > 20 ms is well approximated by d=d0 exp(-t/t) for mixtures of argon-isobutane with benzene or TEA. d0 varies in an approximate linear way with the streamer charge and the systematics of t regarding the high voltage is also presented. Afterpulses are associated not only with wall effects but also with photoionization in the gas mixture itself. Interpretation of the data is attempted
Wed, 01 Feb 1984 00:00:00 GMThttp://hdl.handle.net/10316/129051984-02-01T00:00:00ZSelf-Quenching Streamers in Mixtures with Photoionization Vapourshttp://hdl.handle.net/10316/12899Title: Self-Quenching Streamers in Mixtures with Photoionization Vapours
Authors: Lima, E. P. de; Salete, M.; Leite, S. C. P.; Policarpo, A. J. P. L.; Alves, M. A. F.
Abstract: The basic properties of self-quenching streamers in a proportional counter with a thick anode wire are investigated. In particular, the influence of mixing benzene and triethylamine to argon-isobutane mixtures is studied regarding thresholds for streamer production, pulse shapes and dead time. There is a lowering of the high voltage threshold for streamer production associated with low concentrations of triethylamine and benzene. Higher concentrations of benzene increase that threshold. Triethylamine leads to narrower pulses. Stable operation is observed for a much broader range of high voltages than in the absence of photoionization vapours
Tue, 01 Feb 1983 00:00:00 GMThttp://hdl.handle.net/10316/128991983-02-01T00:00:00ZThe Energy Resolution and Window Area Capabilities of the Gas Proportional Scintillation Counterhttp://hdl.handle.net/10316/12897Title: The Energy Resolution and Window Area Capabilities of the Gas Proportional Scintillation Counter
Authors: Alice, M.; Alves, F.; Policarpo, A. J. P. L.; Salete, M.; Leite, S. C. P.
Abstract: The behaviour of xenon and argon-xenon gas proportional scintillation counters is con sidered. For X-rays, ranges of window area are defined showing competition with semiconductor detectors. Data for primary scintillation of X-rays and alpha particles are included. Relative efficiencies of tetraphenylbutadiene, p-terphenyl, diphenyl-stilbene, sodium salicylate and p-quaterphenyl were measured
Sat, 01 Feb 1975 00:00:00 GMThttp://hdl.handle.net/10316/128971975-02-01T00:00:00ZModelling of an IR scintillation counterhttp://hdl.handle.net/10316/4536Title: Modelling of an IR scintillation counter
Authors: Fraga, M. M. F. R.; Fraga, F. A. F.; Policarpo, A. J. P. L.
Abstract: A systematic study of the excitation and de-excitation mechanisms in ternary gas mixtures Ar+CO2+N2 is presented regarding the possibility of developing a proportional scintillation counter based on the detection of the infrared molecular emissions associated with the lowest vibrational states of molecules. The use of visible or near-infrared photons ([lambda]<1Â [mu]m) for applications like imaging and quality control of microstructure detectors has been reported. In view of these applications we analyse the processes leading to near-infrared emissions in pure argon and give an estimation of the number of photons emitted per electron, at several pressures, as a function of the charge gain.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10316/45362000-01-01T00:00:00ZLow-temperature performance of a large area avalanche photodiodehttp://hdl.handle.net/10316/4476Title: Low-temperature performance of a large area avalanche photodiode
Authors: Solovov, V. N.; Neves, F.; Chepel, V.; Lopes, M. I.; Marques, R. F.; Policarpo, A. J. P. L.
Abstract: A Large Area Avalanche Photodiode was studied, aiming to access its performance as light detector at low temperatures, down to -80°C. The excess noise factor, F, was measured and found to be approximately independent of the temperature. A linear dependence of F on the APD gain with a slope of 0.00239±0.00008 was observed for gains >100. The detection of low intensity light pulses, producing only a few primary electron-hole pairs in the photodiode, is reported.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10316/44762003-01-01T00:00:00ZPerformance of a tracking device based on the GEM scintillationhttp://hdl.handle.net/10316/12909Title: Performance of a tracking device based on the GEM scintillation
Authors: Fraga, F. A. F.; Margato, L. M. S.; Fetal, S. T. G.; Marques, R. Ferreira; Policarpo, A. J. P. L.
Abstract: A tracking device based on gas electron multiplier scintillation using a high-resolution cooled charge-coupled device (CCD) camera was developed. The CCD is sensitive to the 400-1000 nm band, and standard glass photographic lenses are used. The active gas is an Ar-CF4 mixture. The prototype detector is described and images of single alpha tracks are presented. The light yield and detector performance for several other gaseous mixtures, such as 4He-CF4, are also investigated
Fri, 01 Feb 2002 00:00:00 GMThttp://hdl.handle.net/10316/129092002-02-01T00:00:00ZTime analysis of the light pulses on gaseous active scintillators using GEMs with He/CF4http://hdl.handle.net/10316/4479Title: Time analysis of the light pulses on gaseous active scintillators using GEMs with He/CF4
Authors: Margato, L. M. S.; Fraga, F. A. F.; Fetal, S. T. G.; Fraga, M. M. F. R.; Marques, R. Ferreira; Policarpo, A. J. P. L; Guerard, B.; Manzin, G.
Abstract: The time structure of light pulses from GEM detectors operated in scintillation mode with He/CF4 mixtures, previously used with integrating readout devices for neutron detection, has been investigated. A system using photomultipliers (PMs) and charge preamplifiers coupled to a fast digitizer has been used to measure simultaneously both the charge and light signals of the avalanches and the dependence of these signals on the operating conditions of the GEM, such as gain, transfer yield and collection field. The present results show that detectors relying on photon counting techniques, using of position sensitive PMs or arrays of avalanche photodiodes, are most promising as fast position sensitive neutron detectors.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10316/44792003-01-01T00:00:00ZMeasurement of the refractive index and attenuation length of liquid xenon for its scintillation lighthttp://hdl.handle.net/10316/4453Title: Measurement of the refractive index and attenuation length of liquid xenon for its scintillation light
Authors: Solovov, V. N.; Chepel, V.; Lopes, M. I.; Hitachi, A.; Marques, R. Ferreira; Policarpo, A. J. P. L.
Abstract: The attenuation length and refractive index of liquid xenon for its intrinsic scintillation light ([lambda]=178 nm) have been measured in a single experiment. The value obtained for the attenuation length is 364±18 mm. The refractive index is found to be 1.69±0.02. Both values were measured at a temperature of 170±1 K.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10316/44532004-01-01T00:00:00ZQuality control of GEM detectors using scintillation techniqueshttp://hdl.handle.net/10316/4535Title: Quality control of GEM detectors using scintillation techniques
Authors: Fraga, F. A. F.; Fetal, S. T. G.; Marques, R. Ferreira; Policarpo, A. J. P. L
Abstract: Non-destructive quality control of microstructures at the manufacturing stage is an important issue in the foreseen use of huge numbers of such gaseous detectors in the future high luminosity colliders. In this work we report on the use of the scintillation light emitted by the avalanches in GEM channels for checking defects in the foils. The test system is described and data on the relative efficiency of several gaseous mixtures are presented. The foil images obtained with a low-noise CCD system are analysed and compared with the optical images obtained with an industrial inspection system of high magnification. The validity of this test method is established and possible extensions of its use are discussed.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10316/45352000-01-01T00:00:00ZA study of the performance of microstuctures in liquid xenonhttp://hdl.handle.net/10316/4569Title: A study of the performance of microstuctures in liquid xenon
Authors: Lopes, M. I.; Chepel, V.; Marques, R. Ferreira; Policarpo, A. J. P. L.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10316/45691998-01-01T00:00:00ZThe scintillation of GEMS coated with wavelength shiftershttp://hdl.handle.net/10316/4445Title: The scintillation of GEMS coated with wavelength shifters
Authors: Fraga, F. A. F.; Fetal, S. T. G.; Fraga, M. M. F. R.; Balau, E. F. S.; Margato, L. M. S.; Marques, R. Ferreira; Policarpo, A. J. P. L; Sauli, F.
Abstract: The optical readout of GEMs, presented a few years ago, is currently being considered for several detector projects. Although using suitable gaseous mixtures the GEM avalanches emit a large number of photons in the visible and/or NIR regions, many gaseous mixtures of great interest for detectors scintillate mainly in the UV, and the readout of these detectors is usually inefficient or very expensive. In this work we report on the operation of GEMs coated with a wavelength converter. We show that using a GEM with an optimal geometry the wavelength conversion process can be quite efficient and does not degrade the intrinsic position resolution of the detector, an usual drawback of the utilisation of wavelength shifters.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10316/44452004-01-01T00:00:00ZTwo-dimensional readout in a liquid xenon ionisation chamberhttp://hdl.handle.net/10316/4503Title: Two-dimensional readout in a liquid xenon ionisation chamber
Authors: Solovov, V.; Chepel, V.; Pereira, A.; Lopes, M. I.; Marques, R. Ferreira; Policarpo, A. J. P. L.
Abstract: A two-dimensional readout with metal strips deposited on both sides of a glass plate is investigated aiming to assess the possibility of its use in a liquid xenon ionisation chamber for positron emission tomography. Here, we present results obtained with an [alpha]-source. It is shown that position resolution of [less-than-or-equals, slant]1 mm, fwhm, can be achieved for free charge depositions equivalent to those due to [gamma]-rays with energy from 220 down to 110 keV.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10316/45032002-01-01T00:00:00ZLuminescence and imaging with gas electron multipliershttp://hdl.handle.net/10316/4464Title: Luminescence and imaging with gas electron multipliers
Authors: Fraga, F. A. F.; Margato, L. M. S.; Fetal, S. T. G.; Fraga, M. M. F. R.; Marques, R. Ferreira; Policarpo, A. J. P. L.
Abstract: Although the GEM has been mainly used as a gaseous preamplifier device, it has been shown that using suitable gaseous mixtures the avalanches emit a large number of photons, in the UV, visible and/or NIR bands. This scintillation, readout by CCDs, has been used recently for the development of imaging detectors to be used with X-rays, alpha particles and neutrons. The luminescence process in the GEM and a summary of its applications will be presented. The latest developments, including the operation of the GEMs in photon counting mode, will also be referred.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10316/44642003-01-01T00:00:00ZPerformance of an optical readout GEM-based TPChttp://hdl.handle.net/10316/4428Title: Performance of an optical readout GEM-based TPC
Authors: Margato, L. M. S.; Fraga, F. A. F.; Fetal, S. T. G.; Fraga, M. M. F. R.; Balau, E. F. S.; Blanco, A.; Marques, R. Ferreira; Policarpo, A. J. P. L
Abstract: We report on the operation of a GEM-based small TPC using an optical readout. The detector was operated with a mixture of Ar+CF4 using 5.48 MeV alpha particles obtained from a 241Am source and the GEM scintillation was concurrently read by a CCD camera and a photomultiplier. Precision collimators were used to define the track orientation. Qualitative results on the accuracy of the track angle, length and charge deposition measurements are presented.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10316/44282004-01-01T00:00:00ZOptical readout of GEMshttp://hdl.handle.net/10316/4508Title: Optical readout of GEMs
Authors: Fraga, F. A. F.; Margato, L. M. S.; Fetal, S. T. G.; Fraga, M. M. F. R.; Marques, R. Ferreira; Policarpo, A. J. P. L.
Abstract: We present an overview of results from our recent studies on the use of the visible and NIR scintillation emitted by the gas electron multiplier (GEM) and on the possibility of using detectors operated with cascaded GEMs to build tracking chambers.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10316/45082001-01-01T00:00:00ZCCD readout of GEM-based neutron detectorshttp://hdl.handle.net/10316/4500Title: CCD readout of GEM-based neutron detectors
Authors: Fraga, F. A. F.; Margato, L. M. S.; Fetal, S. T. G.; Fraga, M. M. F. R.; Marques, R. Ferreira; Policarpo, A. J. P. L; Guerard, B.; Oed, A.; Manzini, G.; van Vuure, T.
Abstract: We report on the optical readout of the gas electron multiplier (GEM) operated with a gaseous mixture suitable for the detection of thermal neutrons: 3He-CF4. A CCD system operating in the 400-1000 nm band was used to collect the light. Spectroscopic data on the visible and NIR scintillation of He-CF4 are presented. Images of the tracks of the proton and triton recorded with a triple GEM detector are also shown.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10316/45002002-01-01T00:00:00ZGas Proportional Scintillation Counter with Xenon and Xenon Mixtureshttp://hdl.handle.net/10316/12896Title: Gas Proportional Scintillation Counter with Xenon and Xenon Mixtures
Authors: Conde, C. A. N.; Policarpo, A. J. P. L.; Alves, M. A. F.
Abstract: The light output of the recently developed gas proportional scintillation counter - a gas scintillation counter with light multiplication produced by a cylindrical geometry electric field - is investigated for heavy gaseous media under alpha particle excitation with a 56 UVP phototube. The gases used are Xe, and Xe-Ar and Xe-N2 mixtures for a wide range of concentrations, at a total pressure of about 965 Torr. The light output of the Xe-Ar mixtures shifts towards the ultraviolet (¿ ¿ 3250 Å) region as the electric field intensity increases. Xe-Ar mixtures with Xe concentrations ranging from about 1 to 10% give - with a p-quaterphenyl wavelength shifter - a light output more than two orders of magnitude larger than that of a CsI(T1) scintillator. In Xe-N2 mixtures - with wavelength shifter - nitrogen has a quenching effect. For the mixtures of noble gases the rise time of the secondary component of the light pulse is slow, typically 15 ¿s. Methane and nitrogen while having a quenching effect, reduce this rise time
Mon, 01 Jan 1968 00:00:00 GMThttp://hdl.handle.net/10316/128961968-01-01T00:00:00Z